Continental

Problemi valanghivi

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  Loose Wet

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alta quota
  • Limite del bosco
  • Sotto il limite del bosco

  Probabilità

  Likely

  Dimensione

  1–2.5

  Yesterday saw large active wet loose avalanches on steep solar aspects of Snow Slide Gulch and South Three Pigs.  This was due to temperatures that spiked above freezing yesterday and reached into upper elevations.  Expect wet loose activity to continue tomorrow and potentially be more significant.  The degree of overnight freeze on the surface snow, aspect, time of day, and moisture in the surface snow are all important things to pay attention to in order to avoid wet loose hazards.  Timing is becoming more important by the day.

  Steep slopes that are perpendicular to the sun are the most prone to wet loose failure.  Rocky terrain will be the first to react as the rocks absorb the suns' energy and transmit it into the surrounding snow.

  Pay attention to the effect the sun has on the snow surface.  Avoid exposure to steep terrain with wet snow during the heat of the day, this includes the terrain above you, not just the slope you are travelling on.

  

• 

  Wind Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alta quota
  • Limite del bosco
  • Sotto il limite del bosco

  Probabilità

  Possible

  Dimensione

  1–2

  A short North wind event on 3/31 added to the depth of windslabs that had formed the prior week and has formed new slabs in specific areas previously unaffected by wind.  These slabs are not widespread, but do exist on the lee side of some high elevation ridge lines.  Thompson Pass road corridor has more windslabs than more remote zones due to the wind channeling effect of Thompson Pass.  

  Multiple small (D1-1.5) human triggered avalanches have been reported over the last 48 hours involving wind loaded snow.  These have occurred at upper elevations and are small relative to slope size.  On 4/2  wind affected snow on solar aspects was observed to be breaking down due to temperature and becoming wet within the top 2 inches and moist below on slopes below 4000'.

   To avoid this problem, it is important to anticipate where these slabs may exist.  To understand their potential location imagine what slopes would be stripped and which ones would be loaded by a NE wind in the area you are travelling.  Terrain can have a big impact on wind direction, so also look for surface clues on the snow for previous wind direction.  Fresh wind lips point towards lee slopes and eroded snow faces point towards previous wind direction.  Wind slabs will have a rounded smooth look or a rippled texture.  They will also have a hollow drum like feel at this point.  

  The sensitivity of wind slabs is expected to be decreasing, but reactive pockets may still exist, especially where they overlie a melt freeze crust.

  

• 

  Persistent Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alta quota
  • Limite del bosco
  • Sotto il limite del bosco

  Probabilità

  Unlikely

  Dimensione

  1.5–2.5

  For 2 weeks, we have been tracking a layer of buried surface hoar covered by 2 feet of snow near the coast that decreases to only 4 inches at the far northern end of our forecast area. In our core forecast area we have been finding this layer to be unreactive.  Formal snow pits and hasty pits continue to show a layer at the 3/16 new/old interface that consists of highly deformed facets(healing) that are mixed with other grain types that consist of rounds.  Where this setup exists triggering an avalanche at this layer is unlikely.

  We are continuing to talk about this layer due to observations that continue to come in from helicopter operations that are finding this layer much more intact and reactive in stability tests as recently as 3/29, East of Marshall Pass.  Even though this terrain is well outside our forecast area, we want users to be aware of the potentially dangerous setup if they are planning to travel to more remote zones.

  Buried surface hoar can persist and remain active for an extended period. Any area where well-preserved crystals are found below the overlying slab may be capable of producing avalanches for quite some time. Remain diligent and assess the snowpack on a slope-by-slope basis in remote or unfamiliar terrain.  Natural settlement of the overlying slab, temperature increase, and wind can all increase cohesion, which can increase the sensitivity of this weak layer where it is present.  Additional snowfall later this weak has the potential to increase the sensitivity of this layer where it exists.